Hiroki Ago

We have studied the work function and density of states (DOS) of multiwall carbon nanotubes (MWNTs) using ultraviolet photoelectron spectroscopy (UPS). Raw MWNTs were purified by successive sonication, centrifugation, sedimentation, and filtration processes with the aid of a nonionic surfactant. The purified MWNTs showed a slightly lower work function (4.3 eV) than that of highly oriented pyrolytic graphite (4.4 eV). Effects of three different oxidative treatments, air-, oxygen plasma-, and acid

The advantages of combining carbon nanotubes with conjugated polymers for high-efficiency photovoltaic devices are explored in this article. The preparation and optical properties of a composite of multiwalled carbon nanotubes (MWNTs) and poly(p-phenylene vinylene) (PPV) are reported and the efficiency of a photovoltaic device fabricated from the composite investigated. A quantum efficiency approximately twice that of the standard ITO device is reported, believed to be due in part to a complex i

With the profuse amount of two-dimensional (2D) materials discovered and the improvements in their synthesis and handling, the field of 2D heterostructures has gained increased interest in recent years. Such heterostructures not only overcome the inherent limitations of each of the materials, but also allow the realization of novel properties by their proper combination. The physical and mechanical properties of graphene mean it has a prominent place in the area of 2D heterostructures. In this r

Epitaxial chemical vapor deposition (CVD) growth of uniform single-layer graphene is demonstrated over Co film crystallized on c-plane sapphire. The single crystalline Co film is realized on the sapphire substrate by optimized high-temperature sputtering and successive H(2) annealing. This crystalline Co film enables the formation of uniform single-layer graphene, while a polycrystalline Co film deposited on a SiO(2)/Si substrate gives a number of graphene flakes with various thicknesses. Moreov

Graphene has been widely studied for its many extraordinary properties, and other two-dimensional layered materials are now gaining increased interest. These excellent properties make thin layer materials very attractive for integration into a wide variety of technologies, particularly in flexible optoelectronic devices. Therefore, gaining control over these properties will allow for a more focused design and optimisation of these possible technologies. Through the application of mechanical stra

Monolayers of transition metal dichalcogenides (TMDCs) have attracted a great interest for post-silicon electronics and photonics due to their high carrier mobility, tunable bandgap, and atom-thick 2D structure. With the analogy to conventional silicon electronics, establishing a method to convert TMDC to p- and n-type semiconductors is essential for various device applications, such as complementary metal-oxide-semiconductor (CMOS) circuits and photovoltaics. Here, a successful control of the e

For electronic applications, synthesis of large-area, single-layer graphene with high crystallinity is required. One of the most promising and widely employed methods is chemical vapor deposition (CVD) using Cu foil/film as the catalyst. However, the CVD graphene is generally polycrystalline and contains a significant amount of domain boundaries that limit intrinsic physical properties of graphene. In this Perspective, we discuss the growth mechanism of graphene on a Cu catalyst and review recen

Abstract The electrical contact is one of the main issues preventing semiconducting 2D materials to fulfill their potential in electronic and optoelectronic devices. To overcome this problem, a new approach is developed here that uses chemical vapor deposition grown multilayer graphene (MLG) sheets as flexible electrodes for WS 2 field‐effect transistors. The gate‐tunable Fermi level, van der Waals interaction with the WS 2 , and the high electrical conductivity of MLG significantly improve the

We have studied the electronic interaction between photoexcited poly(p-phenylene vinylene) (PPV) and multiwall carbon nanotubes (MWNT's) using photoluminescence (PL) and photoinduced absorption (PIA) spectroscopy. We have found that the MWNT's strongly interact with the photoexcited PPV, while there is no significant interaction in the ground state. The \ensuremath{\pi} conjugation of PPV was slightly reduced in the composite, reflecting the nanoscopic structural influence of the MWNT's. On the

Multilayered heterostructures of two-dimensional materials have recently attracted increased interest because of their unique electronic and optical properties. Here, we present chemical vapor deposition (CVD) growth of triangular crystals of monolayer MoS2 on single-crystalline hexagonal graphene domains which are also grown by CVD. We found that MoS2 grows selectively on the graphene domains rather than on the bare supporting SiO2 surface. Reflecting the heteroepitaxy of the growth process, th

Single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution are synthesized by thermal chemical vapor deposition (CVD) of methane over Fe/MgO catalyst on the basis of parametric study considering Fe loading, reaction temperature and time, methane concentration, and structure of a support material. We found that the porous MgO support gives the SWNTs with a narrow diameter distribution with the mean diameter and standard deviation of 0.93 and 0.06 nm, respectively, only when the Fe

The catalytic growth of single- and double-walled carbon nanotubes (SWNTs and DWNTs) by chemical vapor deposition (CVD) strongly depends on the support material. Not only the presence of nanopores in the support material but also the interaction with metal particles is believed to play an important role. Here, we study the roles of the metal−support interaction by employing iron particles with a mean diameter of 9.8 nm supported on crystalline magnesia (MgO) powder. The crystalline MgO powder ha